i would say the spring inside the filters bypass needs xxx psi to open reguardless of system psi. that would be how much push is on it from the oil flowing agenst it while trying to go through the media.
if you have a bypass i my self like the wix with it in the front so it does not clean all the crap the filter caught. some of the others that bypass from the back and the oil flows past the dirt and resuspends it.
i hope the hp6 is a better filter than the hp1 and 2 i know a couple of people that the ph filters crack and blow oil out or colapse.
i my self stay away from fram on anything important.

all this is how i think of it. i have cut a lot of filters apart to see how cheep they are and how they bypass.